A GLASS COATING COMPOSITION

Abstract

A glass coating composition for a fuel cell gasket is described. The coating comprises: a glass component effective to form an alkaline solution in the presence of an equivalent amount of water by weight, a binder component, a liquid carrier which is greater than 50% by volume: water, and a retarder effective to inhibit hardening of the composition. The glass coating composition is particularly useful in fuel cell gaskets and provides improved resistance to solidification in an aqueous dispersion.

Claims

1. A glass coating composition for a fuel cell gasket comprising: a glass component capable of forming an alkaline solution in an equivalent amount of water by weight; a binder component; a liquid carrier comprising greater than 50% by volume water; and a retarder effective to inhibit hardening of the composition.

2. The glass coating composition of claim 1, wherein the retarder comprises a carbon-free inorganic retarder.

3. The glass coating composition of claim 1, wherein the retarder comprises one or more lignin compounds or salts thereof, hydroxycarboxylic (HC) acids or salts thereof, vinyl polymers, saccharides, zinc oxide, phosphates, fluorates, borates, derivatives thereof, or mixtures thereof.

4. The glass coating composition of claim 1, wherein the retarder comprises a hydroxyl group.

5. The glass coating composition of claim 1 wherein the retarder is water soluble.

6. The glass coating composition of claim 1, wherein the level of retarder in the composition is up to 25 wt % retarder.

7. (canceled)

8. The glass coating composition of claim 1, wherein the gies the glass component is of the type which hardens and sets in water.

9. The glass coating composition of claim 1, wherein the glass component is capable of forming an alkaline solution having a pH of at least 8 in a 1:1 w/w ratio glass:water at 25° C.

10. The glass coating composition of claim 1, wherein the glass component is present in a range of 10-90 wt % of the composition.

11. The glass coating composition of claim 1, wherein a ratio of glass component:retarder is in the range of between 40:1 and 90:1 w/w.

12. The glass coating composition of claim 1, wherein the binder comprises one or more cellulose binders; acrylate homo or copolymers; vinyl acetate homo or copolymers; ethylene copolymers; or polyvinyl butyral.

13. The glass coating composition of claim 1, wherein the level of binder in the composition is in a range of 1 to 20 wt %.

14. The glass coating composition of claim 1, wherein the liquid carrier component comprises at least 70% by volume water.

15. A gasket for sealing two mating surfaces of a fuel cell comprising a core layer, said core layer interposed between a first and second coating layer according to a composition of claim 1.

16. The gasket of claim 15, wherein the core layer is a resiliently deformable core layer comprising one or more platelet fillers.

17. (canceled)

18. (canceled)

19. The gasket of claim 39, wherein the level of the glass component is in a range of between 60 to 99.45 wt %.

20. (canceled)

21. A fuel cell or fuel cell component comprising the gasket of claim 39.

22. (canceled)

23. (canceled)

24. (canceled)

25. A method of producing or sealing a solid oxide fuel cell comprising incorporating the gasket of claim 15 into the solid oxide cell.

26. A method for producing a gasket comprising; a) coating the glass composition of claim 1 onto each of two opposed surfaces of a gasket core layer to form a coated gasket; b) locating the coated gasket in a fuel cell between mating surfaces to be sealed.

27. A method for producing a gasket comprising; a) coating a glass composition according to claim 1 onto each of the mating surfaces to be sealed; b) locating a gasket core layer between the coated mating surfaces to be sealed; c) mating the coated surfaces and interposed gasket core layer together.

28. (canceled)

29. (canceled)

30. (canceled)

31. (canceled)

32. The glass coating composition of claim 3, wherein the retarder comprises a lignosulfonate; a gluconic acid, citric acid, tartaric acid, malic acid, salicyclic acid, glucoheptonate, glucono-delta-lactone, or salt thereof; a sulfonate, carboxylic, or aromatic ring containing vinyl polymer; a phosphoric, polyphosphoric, or phosphosphonic acid or salt thereof; or an alkali borate.

33. The glass coating composition of claim 4, wherein the retarder comprises a sugar selected from monosaccharides, disaccharides, and hydroxylated polysaccharides.

34. The glass coating composition of claim 1, wherein the retarder comprises boric acid or a salt thereof.

35. The glass coating composition of claim 1, wherein the glass component comprises SiO.sub.2, Al.sub.2O.sub.3, B.sub.2O.sub.3, BaO, Bi.sub.2O.sub.3, CaO, Cs.sub.2O, K.sub.2O, La.sub.2O.sub.3, Li.sub.2O, MgO, Na.sub.2O, PbO, Rb.sub.2O, Sb.sub.2O.sub.3, SnO, SrO, TiO.sub.2, Y.sub.2O.sub.3, or ZnO.

36. The gasket of claim 16, wherein the one or more platelet fillers comprises talc, mica, chemically exfoliated vermiculite, or thermally exfoliated vermiculite.

37. The method of claim 26, further comprising heating the gasket.

38. The method of claim 27, further comprising heating the gasket.

39. A gasket for sealing two mating surfaces of a fuel cell, the gasket comprising a core layer interposed between a first coating layer and a second coating layer, wherein the first and second coating layers each comprise a glass component capable of forming an alkaline solution in an equivalent amount of water by weight and a retarder effective to inhibit hardening of the composition.

40. The glass coating composition of claim 1, wherein the retarder comprises sodium metaborate, sodium tetraborate, or potassium pentaborate.

Description

EXAMPLES

[0140] The following glass powders were tested: [0141] 1 VIOX V1467 (pH in 1:1 water dispersion 6-7) [0142] 2 VIOX V2289 (pH in 1:1 water dispersion 6) [0143] 3 FLX 102 (pH in 1:1 water dispersion 10) [0144] 4 FLX 101 (pH in 1:1 water dispersion 10) [0145] 5 Schott GM31107 (pH in 1:1 water dispersion 10.5)

Comparative Test

[0146] For a comparative test, the above glass powders were incorporated into the following composition:

TABLE-US-00001 Glass powder 100 Dispex N40 1 Water 42 1% Natrosol 1 1% Kelzan 1
Dispex N40—wetting and dispersing agent comprising a solution of a sodium salt of methacrylic acid in water.
Natrosol—thickening and suspending agent comprising 1% hydroxyethylcellulose solution.
Kelzan—anti-settling agent comprising 1% xanthan gum solution.

Results of Comparative Test

Comparative Example 1 (Containing VIOX V1467)

[0147] After 2 hours separated into water layer above a packed sediment. Could be re-mixed with effort. No change after 24 hours and no solidification reaction.

Comparative Example 2 (Containing VIOX V2289)

[0148] After 2 hours separated into water layer above soft sediment. Easy to re-mix. No change after 24 hours and no solidification reaction.

Comparative Example 3 (Containing FLX 102)

[0149] Composition started to thicken almost immediately. Pasty consistency after two hours. After 24 hours the composition became a thick coagulated paste that was not recoverable.

Comparative Example 4 (Containing FLX 101)

[0150] After one hour the composition became pasty. After 24 hours the composition had become a very stiff paste which was unusable as a coating.

Comparative Example 5 (Containing Schott GM31107)

[0151] The composition went solid within minutes

[0152] As shown by the above examples, it has been found that alkaline glasses solidify quickly in aqueous dispersions, and as such show poor storage stability.

Inventive Test

[0153] For a test of compositions according to the present invention, the FLX 102 and FLX 101 glass powders were incorporated into the following composition in examples 1 and 2:

TABLE-US-00002 Glass powder 100 Dispex N40 1 Water 42 1% Natrosol 1 1% Kelzan 1 Borax 1.5
Borax—retarder comprising disodium tetraborate.

Results of Inventive Test

Example 1 (Containing FLX 102)

[0154] After two hours the composition formed a packed sediment that could be remixed. The composition was in the same form after 24 hours with no solidification. After 48 hours there was still no solidification.

Example 2 (Containing FLX 101)

[0155] After two hours there was no change in the form of the composition. After 48 hours there was some separation but the composition could be readily remixed and no solidification was found.

[0156] In further inventive example 3, the Schott GM31107 glass powder was incorporated into the following composition:

TABLE-US-00003 Glass powder 100 Dispex N40 1 Water 42.5 1% Natrosol 10 1% Kelzan 10 Borax 1.5 Plextol d498 10 10% yellow 2.2 10% red 0.4 10% black 0.55
Plextol 0498—binder comprising an acrylic dispersion stabilised for application in high alkalinity system.
Yellow pigment—Gemsperse EP83 water based dispersion of organic pigment Yellow 83.
Red pigment—Gemsperse EX166 water based dispersion of organic red pigment.
Black pigment—Gemsperse EP7 water based dispersion of carbon black.

[0157] The above composition was formed by premixing water, Dispex and borax until borax was dissolved. The glass powder was then added with stirring. Preformed Natrosol and Kelzan solutions were then added with slow stirring, followed by the addition of Plextol with slow stirring and finally the pigments with slow stirring.

Results of Inventive Test

Example 3 (Containing Schott)

[0158] The composition produced negligible thickening over 2 days. There was also negligible settling and any settling could be easily re-mixed. It was further found that the composition was suitable for application after 4 days when stored at ambient temperature and for 7 days when stored in a fridge.

[0159] The composition of example 3 was applied to a vermiculite gasket core layer using 50μ KBar (available from RK Print Coat Instruments Ltd, Litington, Royston, SG8 0QZ, UK) to give an even film which was air dried. The dried film was coherent and rub resistant with negligible chalking. The sheet was heated to 370° C. to burn-off the organics. Heating of the sheet to 700° C. produced a clear, transparent melted glass coating.

Further retarders were tested for their efficacy in retarding/stabilising the glass composition. The formulation used was as in example 3 except that borax was replaced as follows:—

Example 4. Ortho Boric Acid (H.SUB.3.BO.SUB.3.)

[0160] Boric acid is an extremely weak acid with a solution ph of 6.7 & is sufficiently soluble in water. Boric acid was dissolved in the water component at a level of 1.4 parts in the above formulation prior to adding the Dispex & glass.

Viscosity was monitored as follows:—
Initial—low viscosity smooth liquid
6 hours—low viscosity smooth liquid
24 hours—low viscosity smooth liquid

Example 5. Sugar (Sucrose)

[0161] Added at 1.4 parts to the above formulation by dissolving in the water prior to adding the glass.

Viscosity monitored as follows:—
Initial—low viscosity liquid
1 hr—sloppy paste
6 hr—thick paste—no grit
24 hr—thick paste—no grit
48 hr—stiff paste but still workable

Example 6 Tartaric Acid

[0162] Added at 1.4 parts to the above formulation by dissolving in the water prior to adding the glass.

Viscosity monitored as follows:—

[0163] Initial—low viscosity liquid

[0164] 7 hrs—creamy consistency

[0165] 24 hrs—creamy consistency

[0166] 72 hrs—creamy consistency, no grit or flocculation

Example 7 Salicylic Acid

[0167] Added at 1.4 parts as previously described.

Viscosity monitored as follows:—

[0168] Initial—low viscosity liquid

[0169] 45 mins—low viscosity liquid

[0170] 24 hrs—sloppy paste, no grit, still workable

[0171] As it can be seen from the above examples, aqueous compositions according to the present invention that contain alkaline glasses and a retarder show improved resistance to solidification in an aqueous dispersion, providing a substantial improvement in storage stability for these high temperature glasses.

[0172] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0173] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0174] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0175] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.